Automatic lubricators of the type having continuously spring biased pistons or plungers have been manufactured and in use for the past half century and originally included a cast metal base having a central axially extending outlet opening through a threaded fitting and a transverse inlet fitting or nipple. A metal grease cup was threaded to this base and formed a reservoir for lubricant entering through the inlet fitting in the base, and a spring biased piston with annular O-ring seals was slidable in the metal cup and biased in a direction to slowly force lubricant from the base through the outlet under the continuous biasing force of a coil compression spring seated in the rear of the cup. These automatic lubricators have found a significant degree of success in lubricating machinery that requires daily or even more frequent lubrication. Since the reservoir holds several cubic inches of lubricant, the maintenance operator fills the reservoirs much less frequently than would otherwise be required to directly lubricate a high demand machine.
Through the years, several successful modifications have been made to this basic automatic lubricator. One such improvement includes a tapered orifice in the base adjacent to the outlet that attempted to achieve the objective of continuous flow from the lubricator as the piston moves forwardly in the cup. Since the spring force decreases as the piston moves forwardly, it had been though that tapering the orifice to increase the area of the orifice as the piston moves forwardly would provide continuous lubrication flow, although some tests have indicated doubt as to whether this in fact takes place in these tapered orifice designs. Another modification in these early automatic lubricators or "automatic grease cups" as they are sometimes referred to, is the provision of an overflow orifice in the cup near its rear end that communicates with the lubricant side of the plunger as the plunger reaches its extreme rear position, to permit lubricant to escape from the cup and thereby minimize the possibility of overfilling and grease cup rupture.
While such vent or overflow holes are effective, they do require additional machining operations in the side of the cup and thereby increase the cost of the overall assembly.
Still another improvement in the original automatic lubricator design, proposed during the last decade, is the provision of a clear plastic reservoir or cup so that the operator can not only visually see when the lubricator is empty, but also can have an idea of when the lubricator is filled during the filling operation by viewing the position of the plunger in the cup.
One disadvantage of these clear plastic grease cups is that because they are constructed of plastic and have closed end grease cups, a core piece is required in the molding operation that must be removed, and hence the inside of the cup must be tapered somewhat for core removal. Since the open end of the cup is usually threaded to the base in these designs, the diameter of the cup increases as the plunger moves forwardly therein, creating the possibility of leakage as the plunger approaches a forward position where spring pressure is low and plunger leakage problem is the greatest.
Plunger misalignment in most of these prior automatic lubricators creates still another sealing problem. Usually the plunger is additionally guided by a central projection to minimize plunger tilting. In all of these prior designs, however, the axial distance between the plunger seal and point of engagement of the central projection varies as the plunger moves or travels in the cup and as the plunger approaches the forward end of the cup, this distance is at a minimum permitting maximum tilting of the plunger at the point in plunger travel where sealing is the most difficult.
The rate of flow of lubricant from the assembly is controlled by the force applied to the piston or plunger by the coil compression spring, and if the flow rate is too high or too low, the maintenance operator simply changes the lubricator spring from one spring rate to another. To do this, in all presently known automatic lubricators, it is necessary to disconnect the cupshaped reservoir from the base, clean the grease from inside the reservoir, remove the greasy plunger, then remove and change springs in the bottom of the cup and then reinsert the piston in the cup and replace the cup. This is a messy and time consuming operation.
In one of the recently devised modifications to the basic automatic lubricator, the base as well as a transparent cup or reservoir are plastic and to increase strength a metal outlet fitting is pressed into the plastic base so that it is rigidified and may be easily attached to an associated machinery threaded receiving bore. A metal inlet fitting is pressed into the side of the plastic base and permits lubricant to be added to the lubricator from conventional lubricant supply valves or "grease guns". The problem in these plastic based lubricator designs is that the operator can easily apply too much transverse force to the inlet fitting during the filling operation and the cantilevered plastic base frequently breaks or cracks, destroying the entire lubricator.
It is the primary object of the present invention to ameliorate the problems noted above in automatic lurication devices.